Receptor Mediated Calcium Entry in Acinar Cells Calcium (Ca2+) is the final messenger coupling cellular stimulation to secretion in acinar cells. Cellular stimulation causes a rise in intracellular Ca2+ concentration ([Ca2+]i) when Ca2+ is released from intracellular stores via the action of soluble second messengers. This release results in the depletion of intracellular Ca2+ stores. Receptor- mediated calcium entry (RMCE) is a process whereby receptor activation mediates calcium entry independently of membrane potential. RCME is observed after agonist stimulation in secretory cells, and is necessary to "refill" calcium stores and to restore cellular responsiveness. A portion of RMCE in secretory cells has been shown to be dependent on the "emptiness" of intracellular calcium stores and will be refereed to here as depletion-activated calcium entry. The long-range goal of this project is to describe the mechanism of depletion-activated calcium entry and the intracellular messengers or mechanisms that are responsible for its regulation. Details about the mechanism of depletion-activated calcium entry, or its regulation, remain unknown. The candidate's preliminary experiments have shown that: a) Depletion-activated calcium entry can be measured in Ca2+ depleted acinar cells using the patch-clamp technique and FURA-2 fluorescence, b) nitroprusside, which raises intracellular cyclic quanosine-3,5-monophosphate, can potentiate calcium entry. The specific aims of the research are: a) to define the regulation of depletion- activated calcium entry by determining how cyclic nucleotides or other messengers act to modulate calcium entry, and b) to determine whether depletion-activated calcium entry is carried by a second messenger-operated Ca2+ channel or by another mechanism such as an ion exchanger; these experiments will use both patch-clamp recording a FURA-2 fluorescence measurements. The suitability and feasibility of the methods have been demonstrated in the preliminary studies. These preliminary studies provide evidence that the proposed experiments will yield useful results. GRANT-R01NS23077 Epilepsy is a major debilitating disorder of the central nervous system which is characterized by abnormal electrical activity of the brain. This disease affects the lives of millions of people. Although epilepsy can be treated in many cases with drug therapy, a significant number of patients are intractable to drug treatment. The aim of this research plan is to determine the cellular mechanisms of epilepsy in humans, in order to assist in developing improved treatments for seizure-disorders. The cellular mechanisms of seizure activity will be investigated by studying the electrical activity which occurs in the dentate gyrus of temporal lobe epileptic patients. The dentate gyrus holds a crucial position in the control of electrical events in the hippocampus, an important site of seizure initiation. The electrical activity of neurons in the dentate gyrus will be examined in brain slices from temporal lobe epileptic patients. The relative influences of excitatory and inhibitory synaptic input, and intrinsic membrane properties on hyperexcitability of the dentate gyrus will be examined. The hypothesis of a longitudinal gradient in hyperexcitability (seizure susceptibility) of the dentate gyrus will be tested by performing physiological recordings at several locations along the dentate gyrus. The interpretation of these physiological observations will be assisted by histological assessment (synaptic reorganization and cell loss) of tissue from the same regions. The results from the proposed experiments will provide greatly needed information concerning the physiological basis of seizure disorders.